The present invention relates in general to loudspeaker systems and more particularly concerns a novel loudspeaker system characterized by unusually realistic reproduction of sound that is compact and relatively easy and inexpensive to manufacture in large quantities while maintaining good quality control and producing relatively high sound levels in response to relatively low input electrical power levels. The present invention achieves the performance level of the internationally famous BOSE 901 DIRECT/REFLECTING loudspeaker system described in Bose U.S. Pat. No. 3,582,553 and embodies the principles of that patented invention and the invention described in Bose U.S. Pat. No. 3,038,964.
Both that system and a preferred embodiment of this system include eight speakers on a pair of rear panels or baffles that each form an angle of about 30.degree. with the wall upon which the rear speakers direct their sound and one speaker on the front panel or baffle that faces the normal listening area. This arrangement radiates the desired ratio of about 8:1 reflected sound to direct sound while projecting the image of a musical performance located on a stage that is about a foot behind the wall when the enclosure is about a foot in front of the wall so that it is possible to hear the full stereo spread from a wide range of listening positions including directly in front of one enclosure. That system and a preferred embodiment of the present invention also both include an active equalizer for establishing essentially uniform acoustic power radiation as a function of frequency over substantially the entire audio frequency range.
The BOSE 901 loudspeaker system has received an unprecedented series of rave reviews in the United States and many other countries. While that system performs well when driven with power amplifiers of moderate capacity, higher power amplifiers are required to produce high acoustic levels at the lower audio frequencies.
It is known in the prior art to use ported enclosures to obtain higher acoustic power levels at lower frequencies with a given electrical input power. And a simple port works satisfactorily in a conventional woofer-tweeter loudspeaker system and is used, for example, in the BOSE Model 301 DIRECT/REFLECTING loudspeaker system. However, it was discovered that simply porting the loudspeaker cabinet in the system described in U.S. Pat. No. 3,582,553 did not provide satisfactory performance. It was discovered that in the vicinity of port resonance all the small loudspeaker did not operate in phase with the result that the excursions of the drivers working together increased to compensate for the excursions of the out-of-phase drivers, causing the drivers to enter the nonlinear region of operation at relatively modest sound levels.
Accordingly, it is an important object of the invention to provide an improved loudspeaker system.
It is another object of the invention to achieve the preceding object while retaining all the performance advantages of the BOSE 901 loudspeaker system described in U.S. Pat. No. 3,582,553.
It is a further object of the invention to achieve one or more of the preceding objects while increasing the ratio of acoustic power radiated to input electrical power in the bass frequency range.
It is a further object of the invention to achieve one or more of the preceding objects with a compact ported cabinet.
It is still a further object of the invention to achieve one or more of the preceding objects with a structure that is relatively inexpensive and easy to manufacture through mass production techniques while maintaining high quality control.
It is a further object of the invention to achieve one or more of the preceding objects with multiple in-phase-connected full-range loudspeakers in a ported enclosure while solving the problem noted above.